351 rod & main bearing oil clearance

[jagbucket]

trying to do final assembly on the 408 stroker but it seems like murphy is still at it . I can only plastic gauge the bearings and i get 0015 rods and 002 on the mains from the general rule of 1 thou per inch of diameter i should be 0021 and 003 min. although a search on this site states that im within spec. not a high rpm build but still want it to last and not burn. what do you guys think and the best way to correct thanks for the help.

 

[jsfrv6]

You really need to verify your readings. Maybe take to a shop with the correct tools to check your parts. If still too tight, which the readings you listed are too tight, they make extra clearance bearings for that purpose.. But yea, .001 per inch of diameter is a good starting point. My 408 clearances are .0029-.0032 on a 3" main and .0025-.0026 on the 2.1" rods... Been running good for years on 5W-30 oil.. You gotta get this right!

 

[jagbucket]

yes its going back monday i don't understand why the machine shop sent it out this way. your numbers sound right and agree with other info i have found via google

 

[nvrstuk]

Agree that you should have the shop look at it again...

 

[Broncobowsher]

The machine shop probably didn't do anything. All new parts (crank and bearings), should be in spec by the manufacturer. Did you ask/pay the shop to blueprint the new parts?

I would also be contacting the manufacturer of your stroker kit and ask what specs they recommend. Don't tell them your specs up front, get what they say they should be first. If they don't match what you have, then bring it to there attention. Not knowing the kit, they may have speced tight clearances for some reason we don't know. But before you send the parts to be reworked, you better check with the supplier of the parts first. Otherwise you might be throwing away any warranty with the parts.

 

[Viperwolf1]

Ford's own 351W specs (both rod and main).
-Desired .0008-.0015
-Allowable .0008-.0026

Nothing wrong with your numbers.

 

[1strodeo]

Ford's own 351W specs (both rod and main).
-Desired .0008-.0015
-Allowable .0008-.0026

Nothing wrong with your numbers.

good info hope to start assembly of my 351 this week thanks

 

[jagbucket]

viper that is the same info i found on searching this site but seems to contradict the .001 per inch of journal diameter perhaps for 6500 and up race motors ? if these Numbers are fine for stock rpms i will be a happy camper. Just trying to clear it up now before final assembly. always reassuring to see higher oil pressure .
the initial job was to send back a motor ready to build and he did charge for "final polish of the crank" also the rods/caps were torqued as though to obtain a measurement .
thanks for the info i can only hope the the shop used the same and is what they intended because it seems to be consistent on all journals

 

[Viperwolf1]

Yes, high rpm motors need more clearance for several reasons. A result of that is decreased engine life.

 

[B RON CO]

Hi, I'll give you some info I've learned.
If the torque spec for the rod bolt is 40 - 50 ft.lb, try the plasti gauge at 45 ft.lb.
If the clearance is a little tight, recheck the clearance at 40 ft.lb.
You may find out there is good clearance.
Good luck

 

[pcf_mark]

Those tolerances are solid for a street engine. It will have amazing oil pressure (as long as the rod side clearance are in spec .015-.020).

 

[jagbucket]

Yeah l did not tear it down yet pending a call to the shop monday. I'm starting to feel better about the specs. Also checking with torque at 42.5 on rods.
The build has always been for heathly street trail rig. Just wasn't expecting such a difference in bearing clearance based on end use. To be fair I've never built anything but stock motors and depended on a machine shop to set clearances to stock . this one with all forged aftermaket parts has me questioning every part I've already had to buy two sets of rods and custom order pistions so the only part from the kit I kept was the crank, now I'm questioning that.
In retro I wish I had bought from local venders. easier contact exchange if needed

 

[jsfrv6]

Jagbucket: here's a good article on clearances...http://www.superchevy.com/how-to/engines-drivetrain/4380-bearing-clearance-info/

 

[73azbronco]

also when doing plastigauge really make sure all the parts are clean dry zero oil front and back.

 

[jagbucket]

just got back from machinists to have an accurate measurement and its at .0022 for rods and the mains are averaging .002 . i guess the only thing plastic can tell is if you need to check further. for peace of mind im glad to have it checked out.

 

[Blue Bastard]

Peace of mind is a comfortable feeling! Glad it was good to go.


Sent from my iPhone using Tapatalk

 

[nvrstuk]

Great, that's why it was good to have the shop look at it again...otherwise you would always be guessing and worrying about it. Now you're good to go...